Multilayer ceramic capacitor

ABSTRACT

In a multilayer ceramic capacitor including first and second inner electrodes alternately arranged with respect to a stacking direction of a multilayer body, a polarity based on a direction of voltage applied between a first outer electrode and a second outer electrode is determined such that the first inner electrodes function as positive electrodes and the second inner electrodes function as negative electrodes. The first inner electrodes have a first metal composition including Ni and Sn, and the second inner electrodes have a second metal composition including Ni. The second metal composition of the second inner electrodes may consist of Ni, or may include Ni as a main component and at least one metal element selected from Au, Pt, Ir, Pd, Os, Ag, Rh, Ru, and Cu, which have standard electrode potentials higher than that of Ni.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2021-058923 filed on Mar. 31, 2021 and is a Continuationapplication of PCT Application No. PCT/JP2022/015246 filed on Mar. 29,2022. The entire contents of each application are hereby incorporatedherein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a multilayer ceramic capacitor, inparticular, to a metal composition of an inner electrode of a multilayerceramic capacitor.

2. Description of the Related Art

Recent development in electronic technology requires multilayer ceramiccapacitors with smaller size and higher capacitance. In order to meetthese requirements, dielectric layers of multilayer ceramic capacitorsare becoming thinner. However, thickness reduction of dielectric layersrelatively increases the intensity of electric field applied to eachlayer. Therefore, it is desirable to improve reliability during voltageapplication.

In general, a multilayer ceramic capacitor includes a multilayer bodythat includes multiple dielectric layers that are stacked on top of eachother and multiple inner electrodes disposed along interfaces betweenthe dielectric layers, and multiple outer electrodes that are formed onouter surfaces of the multilayer body and are electrically connected tothe inner electrodes. Here, there is a known inner electrode thatincludes Ni as a main component, as described in Japanese UnexaminedPatent Application Publication No. 11-283867.

SUMMARY OF THE INVENTION

However, the issue with the inner electrode including Ni as a maincomponent is that the reliability during voltage application isinsufficient to meet the recent demand for miniaturization and highercapacitance.

Preferred embodiments of the present invention provide multilayerceramic capacitors that each have thinner dielectric layers and exhibitexcellent reliability even when voltage of a high electric fieldintensity is applied.

A multilayer ceramic capacitor according to the present inventionincludes a multilayer body that includes multiple dielectric layers thatare made of a ceramic and are stacked on top of each other, and multipleinner electrodes along interfaces between the dielectric layers, andmultiple outer electrodes on outer surfaces of the multilayer body andelectrically connected to the inner electrodes.

The inner electrodes include multiple first inner electrodes andmultiple second inner electrodes that are alternately arranged withrespect to a stacking direction of the multilayer body, and the outerelectrodes include a first outer electrode electrically connected to thefirst inner electrodes and a second outer electrode electricallyconnected to the second inner electrodes.

In a preferred embodiment of the present invention, a polarity based ona direction of voltage applied between the first outer electrode and thesecond outer electrode is determined such that the first innerelectrodes function as positive electrodes and the second innerelectrodes function as negative electrodes, the first inner electrodeshave a first metal composition including Ni and Sn, and the second innerelectrodes have a second metal composition including Ni.

Note that the first metal composition and the second metal compositionare different from each other in terms of at least one of the types andcontents of the constituent elements.

According to preferred embodiments of the present invention, insulationdegradation of a multilayer ceramic capacitor during voltage applicationis reduced or prevented, and thus multilayer ceramic capacitors eachwith excellent reliability can be obtained.

In addition, since the first metal composition of the first innerelectrodes includes Sn, the reliability of the multilayer ceramiccapacitor during voltage application is further improved.

Moreover, since the first and second inner electrodes include Ni, themelting point can be increased compared to the case where Cu is the maincomponent, for example. Therefore, the first and second inner electrodescan be made thinner, the number of layers stacked can be increased whilemaintaining the external dimensions of the multilayer ceramic capacitor,and thus, the obtained electrostatic capacitance can be increased.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically showing a multilayerceramic capacitor 1 according to a preferred embodiment of the presentinvention.

FIG. 2 is a diagram showing standard electrode potentials of metalelements included in first inner electrodes (positive electrodes) 4 andsecond inner electrodes (negative electrodes) 5 in the multilayerceramic capacitor 1 illustrated in FIG. 1 .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The structure of a multilayer ceramic capacitor 1 according to apreferred embodiment of the present invention will now be described withreference to FIG. 1 .

The multilayer ceramic capacitor 1 includes a multilayer body 2. Themultilayer body 2 includes multiple dielectric layers 3 that are made ofa ceramic and are stacked on top of each other, and multiple innerelectrodes 4 and 5 that are disposed along interfaces between thedielectric layers 3. The inner electrodes 4 and 5 are classified intomultiple first inner electrodes 4 and multiple second inner electrodes 5that are alternately arranged with respect to the stacking direction ofthe multilayer body 3. An outer electrode 6 and an outer electrode 7 arerespectively disposed on outer surfaces, more specifically, opposing endsurfaces, of the multilayer body 2. The outer electrodes 6 and 7 areclassified into a first outer electrode 6 electrically connected to thefirst inner electrodes 4, and a second outer electrode 7 electricallyconnected to the second inner electrodes 5.

The compositions of the inner electrodes 4 and 5 are described below.The outer electrodes 6 and 7 include, for example, Ag or Cu as a maincomponent of the conductive component. The dielectric layers 3preferably include a dielectric ceramic that includes, as a maincomponent, a perovskite compound that includes Ba and Ti (however, someof Ba may be substituted with Ca, and some of Ti may be substituted withZr). In particular, high permittivity is exhibited when the maincomponent of dielectric layers 3 is BaTiO₃, and the multilayer ceramiccapacitor 1 exhibits excellent reliability. Note that the dielectriclayers 3 may include, in addition to the aforementioned main component,rare earth elements, Mn, Mg, Si, etc., for example, as sub components.

The raw material powder of the dielectric ceramic is, for example,produced by a solid phase synthesis method. Specifically, first,compound powders of oxides, carbonates, etc., that include constituentelements of the main component are mixed in predetermined proportionsand calcined. Instead of the solid phase synthesis method, ahydrothermal method and other appropriate methods may be applied. Here,the dielectric ceramic may include alkali metals, transition metals, Cl,S, P, Hf, etc., as long as the amounts thereof do not obstruct theadvantageous effects of the present invention.

The multilayer ceramic capacitor 1 is, for example, produced as follows.A ceramic slurry is prepared by using raw material powder of thedielectric ceramic obtained as described above. Next, ceramic greensheets are formed by a sheet forming method or the like. Next, aconductive paste that will form the inner electrodes 4 and 5 areapplied, by printing or the like, to particular ceramic green sheetsselected from among these ceramic green sheets. Then the ceramic greensheets are stacked on top of each other and pressure-bonded to obtain agreen multilayer body. Next, the green multilayer body is fired. In thisfiring step, dielectric layers 3 including a dielectric ceramic areobtained. Subsequently, outer electrodes 6 and 7 are formed on endsurfaces of the multilayer body 3 by baking or the like.

One of the unique features of the multilayer ceramic capacitor 1 is thatthe polarity based on the direction of the voltage applied between thefirst outer electrode 6 and the second outer electrode 7 is determinedsuch that the first inner electrodes 4 function as positive electrodesand the second inner electrodes 5 function as negative electrodes inactual use. Therefore, although not illustrated, a mark that indicatesthe polarity is preferably put on, for example, an outer surface of themultilayer ceramic capacitor 1.

In this regard, a multilayer ceramic capacitor according to a preferredembodiment of the present invention is not limited to the two-terminaltype equipped with the first outer electrode 6 and the second outerelectrode 7 as shown in FIG. 1 , but may also be a multi-terminal typeequipped with three or more outer electrodes. In this case, the voltagemay be applied between particular two sets of outer electrodes selectedfrom among the three or more outer electrodes, in other words, betweenat least one first outer electrode and at least one second outerelectrode, such that the first inner electrodes function as positiveelectrodes and the second inner electrodes function as negativeelectrodes.

Another of the unique features of the multilayer ceramic capacitor 1 isthat the metal compositions of the first inner electrodes 4 and thesecond inner electrodes 5 are selected as follows. That is, the firstinner electrodes 4, which function as positive electrodes, have a firstmetal composition including Ni and Sn, and the second inner electrodes5, which function as negative electrodes, have a second metalcomposition including Ni.

Such a choice of the metal compositions of the first inner electrodes 4and the second inner electrodes 5 is based on the following findings.

Although the insulation degradation mechanism of typical multilayerceramic capacitors is not yet elucidated, it is known that negativeelectrode segregation of oxygen ions (positive electrode segregation ofoxygen vacancies) caused by voltage application triggers thedegradation. Therefore, it is expected that the insulation degradationof the multilayer ceramic capacitor can be reduced or prevented byreducing or preventing the negative electrode segregation of oxygenions. In this regard, a possible approach is to have positive electrodesinclude an element that gives a stable oxide and to have negativeelectrodes include an element that gives unstable oxide. According tothis idea, negative electrode segregation can be reduced or prevented byallowing reduction reactions (release of oxygen ions) to occur in thenegative electrodes.

More specifically, regarding the metal compositions of the first innerelectrodes 4 and the second inner electrodes 5, metal elements that havea tendency to undergo an increase in valency (low standard electrodepotential) are used in the first inner electrodes 4 that function aspositive electrodes, and metal elements that have a tendency to undergoa decrease in valency (high standard electrode potential) are used inthe second inner electrodes 5 that function as negative electrodes. Astandard electrode potential is a value inherent to the element, thelower the value, the more stable the oxide, and the higher the value,the more unstable the oxide.

That is, as illustrated in FIG. 2 , the second inner electrodes 5 thatfunction as negative electrodes are to include metal elements havingstandard electrode potentials higher than the standard electrodepotentials of the metal elements in the first inner electrodes 4 thatfunction as positive electrodes. In FIG. 2 , the standard electrodepotential of the first metal composition of the first inner electrodes 4functioning as positive electrodes is to be within the range A, and thestandard electrode potential of the second metal composition of thesecond inner electrodes 5 functioning as negative electrodes is to bewithin the range B.

The standard electrode potentials of the metal elements that can beincluded in the metal compositions of the inner electrodes 4 and 5 are,in the ascending order:

-   -   −0.26 V for Ni,    -   −0.14 V for Sn,    -   +0.34 V for Cu,    -   +0.46 V for Ru,    -   +0.76 V for Rh,    -   +0.8 V for Ag,    -   +0.9 V for Os,    -   +0.92 V for Pd,    -   +1.16 V for Ir,    -   +1.19 V for Pt, and    -   +1.52 V for Au.

Whereas the standard electrode potentials of Ni and Sn included in thefirst metal composition of the first inner electrodes 4 are,respectively, −0.26 V and −0.14 V, the standard electrode potential ofNi included in the second metal composition of the second innerelectrodes 5 is −0.26 V. Here, Ni readily becomes passive, which is aninoxidizable state, and although the standard electrode potentialthereof is described to be −0.26 V, the standard electrode potential canbe deemed substantially 0 V. Thus, when comparing the standard electrodepotential between the first inner electrodes 4 and the second innerelectrodes 5, the reference for the first inner electrodes 4 is thestandard electrode potential of Sn, −0.14 V, and the reference for thesecond inner electrodes 5 is substantially 0 V due to passivation of Ni.

Thus, according to this preferred embodiment, since the standardelectrode potential of the second inner electrodes 5 functioning asnegative electrodes is higher than the standard electrode potential ofthe first inner electrodes 4 functioning as positive electrodes, thenegative electrode segregation of oxygen ions (positive electrodesegregation of oxygen vacancies) caused by voltage application isreduced or prevented by utilizing the redox reactions in the innerelectrodes 4 and the inner electrodes 5. As a result, the insulationdegradation of the multilayer ceramic capacitor 1 during voltageapplication can be reduced or prevented, and a multilayer ceramiccapacitor 1 having excellent reliability can be obtained.

As mentioned above, the second metal composition of the second innerelectrodes 5 may consist of Ni. However, preferably, Ni is included as amain component and at least one metal element selected from Au, Pt, Ir,Pd, Os, Ag, Rh, Ru, and Cu, which have standard electrode potentialshigher than that of Ni, is included as an additive component. Au, Pt,Ir, Pd, Os, Ag, Rh, and Ru included in the second metal composition arenoble metals.

Regarding the metal compositions of the inner electrodes 4 and 5, the“main component” refers to a metal element having the highest contentamong all metal elements, more specifically, a content higher than orequal to 50%.

In the aforementioned preferred embodiment, whereas the standardelectrode potentials of Ni and Sn included in the first metalcomposition of the first inner electrodes 4 are, respectively, −0.26 Vand −0.14 V, the standard electrode potentials of Au, Pt, Ir, Pd, Os,Ag, Rh, Ru, and Cu, which are additive components in the second metalcomposition of the second inner electrodes 5, are all higher than thatof Sn.

Thus, at least one metal element selected from Au, Pt, Ir, Pd, Os, Ag,Rh, Ru, and Cu added to the second metal composition of the second innerelectrodes 5 functioning as negative electrodes can induce morereduction reactions in the second inner electrodes functioning asnegative electrodes and thus can further reduce or prevent negativeelectrode segregation of oxygen ions.

As mentioned above, the higher the standard electrode potential, themore unstable the oxide. Thus, the effect of reducing or preventing thenegative electrode segregation of oxygen ions brought about by the metalelements that can be included as additive components in the second metalcomposition of the second inner electrodes 5 described above increasesin the order of Cu, Ru, Rh, Ag, Os, Pd, Ir, Pt, and Au, which is theascending order of the standard electrode potential.

Furthermore, the first metal composition of the first inner electrodes 4is preferably free of metal elements having standard electrodepotentials higher than that of Sn. This is because the first metalcomposition can advantageously retain the relatively low standardelectrode potential.

Moreover, since the first metal composition of the first innerelectrodes 4 and the second metal composition of the second innerelectrodes 5 both include Ni, for example, compared to the case in whichCu is included as a main component, the melting point can be increased.Thus, the first inner electrodes 4 and the second inner electrodes 5 canbe made thinner, the number of layers stacked can be increased whilemaintaining the external dimensions of the multilayer ceramic capacitor1, and thus, the obtained electrostatic capacitance can be increased.

It should be noted that Ni and Sn included in the first metalcomposition of the first inner electrodes 4 are included in theconductive paste applied to the ceramic green sheets used to produce themultilayer ceramic capacitor 1. Here, Ni and Sn may be preliminarilyprepared as an alloy or intermetallic compound including Ni or Sn andthen included in the conductive paste, or may be separately included inthe conductive paste. In addition, when multiple metal elements areincluded in the second metal composition of the second inner electrodes5, these metal elements may be preliminarily prepared as an alloy orintermetallic compound including these metal elements, or may beseparately included in the conductive paste.

In addition, in the multilayer ceramic capacitor 1 obtained as aproduct, Ni and Sn included in the first metal composition of the firstinner electrodes 4 are preferably alloyed. Similarly, when the secondmetal composition of the second inner electrodes 5 includes multiplemetal elements, these multiple metal elements are preferably alloyed inthe multilayer ceramic capacitor 1 as a product.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A multilayer ceramic capacitor comprising: amultilayer body including a plurality of dielectric layers that are madeof a ceramic and are stacked on top of each other, and a plurality ofinner electrodes along interfaces between the plurality of dielectriclayers; and a plurality of outer electrodes on outer surfaces of themultilayer body and electrically connected to the plurality of innerelectrodes; wherein the plurality of inner electrodes include aplurality of first inner electrodes and a plurality of second innerelectrodes that are alternately arranged with respect to a stackingdirection of the multilayer body; the plurality of outer electrodesinclude a first outer electrode electrically connected to the pluralityof first inner electrodes and a second outer electrode electricallyconnected to the plurality of second inner electrodes; a polarity basedon a direction of voltage applied between the first outer electrode andthe second outer electrode is determined such that the plurality offirst inner electrodes function as positive electrodes and the pluralityof second inner electrodes function as negative electrodes; the firstinner electrodes have a first metal composition that includes Ni and Sn;and the second inner electrodes have a second metal composition thatincludes Ni.
 2. The multilayer ceramic capacitor according to claim 1,wherein the second metal composition of the second inner electrodesconsists of Ni.
 3. The multilayer ceramic capacitor according to claim1, wherein the second metal composition of the second inner electrodesincludes Ni as a main component, and at least one metal element selectedfrom Au, Pt, Ir, Pd, Os, Ag, Rh, Ru, and Cu, which have standardelectrode potentials higher than that of Ni, as an additive component.4. The multilayer ceramic capacitor according to claim 1, wherein thefirst metal composition of the first inner electrodes does not include ametal element having a standard electrode potential higher than that ofSn.
 5. The multilayer ceramic capacitor according to claim 1, whereinthe first outer electrode and the second outer electrode include Ag orCu.
 6. The multilayer ceramic capacitor according to claim 1, whereinthe plurality of dielectric layers include as a main component aperovskite compound including Ba and Ti.
 7. The multilayer ceramiccapacitor according to claim 6, wherein some of Ba is substituted withCa.
 8. The multilayer ceramic capacitor according to claim 6, whereinsome of Ti is substituted with Zr.
 9. The multilayer ceramic capacitoraccording to claim 1, wherein the plurality of dielectric layers includeBaTiO₃.
 10. The multilayer ceramic capacitor according to claim 1,wherein the plurality of dielectric layers include a dielectric ceramicand at least one of rare earth elements, Mn, Mg, or Si.
 11. Themultilayer ceramic capacitor according to claim 1, wherein the pluralityof dielectric layers include at least one of alkali metals, transitionmetals, Cl, S, P or Hf.
 12. The multilayer ceramic capacitor accordingto claim 1, wherein the multilayer ceramic capacitor is a two-terminalcapacitor.
 13. The multilayer ceramic capacitor according to claim 1,wherein the multilayer ceramic capacitor is a multi-terminal capacitorincluding three or more outer electrodes.
 14. The multilayer ceramiccapacitor according to claim 1, wherein the second composition of theplurality of second inner electrodes includes multiple metal elements.15. The multilayer ceramic capacitor according to claim 14, wherein themultiple metal elements in the second composition are alloyed as aproduct.
 16. The multilayer ceramic capacitor according to claim 1,wherein the first composition of the plurality of first inner electrodesincludes multiple metal elements.
 17. The multilayer ceramic capacitoraccording to claim 16, wherein the multiple metal elements in the firstcomposition are alloyed as a product.